Articles made from polyurethane elastomeric filament-containing blended weft knit fabrics are widely used on account of their high stretch, good recovery from extension, and good fit. However, when repeatedly stretched, a polyurethane elastomeric filament-containing blended weft knit fabric will deform and lose its uniformity, readily giving rise to problems such as the above-described deformation, yarn slippage, corrugation, fraying, running, curling and slip-in.
These problems are generally dealt with by folding back the edge of the knit fabric or by sewing another fabric or stretch tape to the fabric edge. However, because of concerns over dermatosis from direct contact by the wearer's skin with raised areas, steps and seams in the fabric, and also because of unresolved problems such as diminished feel and comfort when worn and loss of aesthetics due to visible effects on accompanying outerwear, a desire has existed for knit fabrics which can be used as cut without having to sew the cut edges of the fabric.
Various methods have been found for rendering knit fabrics directly into manufactured articles without sewing the fabric edges. In warp knit fabrics, innovations such as increasing the density of the fabric or modifying the fabric structure have led to knit fabrics which can be used “as cut.” Weft knit fabrics are generally subject to fraying and have a low density. Yet, although methods do exist to prevent fraying by modifying the knit structure to what is referred to as an edging stitch, it has not been possible to render weft knit fabrics directly “as cut” into manufactured articles. Moreover, in methods for manufacturing articles that involve changing the knit structure, such an approach represents a major obstacle to increased productivity and lower costs. Hence, there is a very considerable desire for weft knit fabrics which are capable of being free cut and can be used directly as cut.
It has been proposed that fibers be thermally fused to each other to reduce deformation, yarn slippage, corrugation, fraying, running and curling. In attempts where the heat setting temperature has been raised so as to thermally fuse the typically high-melting polyurethane elastomeric filaments at crossover points therebetween, the need to carry out heat setting at a high temperature has led to undesirable changes in tactile qualities and a lower colorfastness, including specifically yellowing and a hardening in the hand of the fibers with which the polyurethane elastomeric filaments are used. Another problem has been an insufficient degree of thermal fusion and thus substantial separation at thermal fusion sites, resulting in a loss in the ladder-resisting and fray-preventing effects when the article is worn and during laundering. Moreover, lowering the heat-setting temperature leads to a complete loss of the thermal fusing effect.
If special polyurethane elastomeric filaments which fuse at a low temperature are used, these filaments can be fused at a low heat-setting temperature of 140 to 160° C. However, the other yarns with which they are knit do not set to a sufficient degree, giving rise to problems such as creasing of the greige fabric and uneven dyeing. On the other hand, if heat setting is carried out within a temperature range at which the other yarns used in knitting can set properly, the low temperature-fusing elastomeric filaments will experience a large decline in strength within the knit fabric, lowering the recovery of the fabric from extension and leading to yarn breakage within the heat-set fabric. Another problem that remains is that, even were it possible to strongly fuse the filaments at a low temperature, the fabric thus obtained, when used as a conventional single-knit weft knit fabric, for example, would harden as a result of heat setting.
By using a low-melting filaments other than polyurethane, fusion can be achieved at a setting temperature of 130 to 185° C. (see JP-B 2-8058 and JP 2001-164444 A). However, when fusion is effected using such low-melting filaments, the fusion and the hardening of the fibers combine to make the hand of the fabric even harder, thus detracting from the comfort of the article when worn and in extreme cases even causing dermatosis and greatly diminishing the stretch.
JP-A 2001-159052 discloses a method for preventing yarn slippage by heat treating at 200° C. a fabric knit from two types of polyether ester elastomeric filaments having different melting points. However, compared with polyurethane elastomeric filaments, polyether ester elastomeric filaments have a less than satisfactory performance in terms of stretch properties such as extensibility and recovery from extension, and thus leave much to be desired.